Apparatus providing magnetic fields for electron discharge tubes



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GRID C'ATHODE POTENTIALS T1 TZA WWW m M Sept. 26, 1950 D. v. EDWARDS APPARATUS PROVIDING MAGNETIC mzws FOR mzc'mon DISCHARGE TUBES 4 Sheets-Sheet 4 Filed Dec. 16, 1947 Fl 60 E n A.C.VOLTAGE Fl 6.. SF. VOLTAGES ACROSS TUBES TIA TEA

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@154 ATTORNEY Patented Sept. 26, 1950 APPARATUS PROVIDING MAGNETIC FIELDS FOR ELECTRON DISCHARGE TUBES Donald V. Edwards, Montclair, N. J., minor to General Railway Signal Company, Rochester,

Application December 16, 1947, Serial No. 792,010

This invention relates to apparatus and circuits employing electron discharge tubes, and more particularly to power conversion apparatus employing grid control hard vacuum tubes, such as power amplifiers, oscillators, control rectifiers, inverters and the like. 7

In various types of circuits involving the use of hard Vacuum grid control tubes, it is desirable to employ a type of tube, conveniently termed a magnatriode, which has a magnetic field enablingthe grid of the tube to assume relatively high positive potentials without significant or objectionable electron current to the grid. A tube of this magnatriode type is disclosed, for example, in the application of J H. Burnett, Ser. No. 647,007, filed February 12, 1946. In certain types of power conversion apparatus for converting alternating current to direct current or vice versa, such as disclosed for example in my prior application Ser. No. 734,965, filed March 15, 1947, in which the magnatriod'e type of tube may be used to advantage, an inductor or reactor is included in the anode circuits of the tubes; and for many applications and uses, this inductor is of the iron core type with a relatively large inductance.

Taking into consideration such conditions, where the tubes used require a magnetic field, and the circuit organization involves an inductor of relatively large inductance and capable of providing a magnetic field, it is proposed in accordance with this invention to provide an arrangement or combination of circuit elements for power conversion apparatus of this character, in which the magnetic field created by the flow of current conducted by the tubes through the inductor is used to provide the magnetic field required for these tubes, rather than a separate magnetizing coil or permanent magnet. In such an organization, the intensity or strength of the magnetic field for the magnatrlode type of tubes varies with the average current conducted by these tubes and flowing through the inductor; and the primary purpose and object of this invention is to provide an arrangement of circuit elements for such acircuit organization, including a form of grid control for the tubes, which will give satisfactory and efficient operation of the tubes under such conditions. Various other characteristic features, attributes and advantages of the circuit organization of this invention will be in part apparent, and in part pointed out as the description progresses.

Generally speaking, and without attempting to define the nature and scope of the invention, it is proposed to provide an organization and arrangement of circuit elements for power conversion apparatus of the character under consideration, including regulation or control of the positive potentials for the grids of tubes of the magnatriode type, in which the magnetic field of an inductor energized by the current conducted by the tubes may be used advantageously and effectively to serve as the magnetic field for these tubes. In

16 Claims. (Cl. 321-38) the circuitorganization or combination characterlstic of this invention, both the tubes and the inductor employed may take any suitable form adapted for the particular situation and operating conditions; and it should be understood that the particular structure of tube and inductor, and the specific circuit arrangement herein illustrated and described, are merely typical or representative of the type of tube, inductor and circuit arrangement that may be employed in accordance with this invention.

Although the invention may take a wide variety of forms in practice, its general nature and charactertistics are exemplified in the specific embodiment shown in the accompanying drawings, in which the parts and circuits are illustrated schematically and conventionally, more with a view of facilitating an understanding of the nature of the invention, than for the purpose of showing in detail a particular arrangement and construction of parts preferably adopted in practice.

In the accompanying drawing, Fig. 1 is a schematic illustration of the tube elements of one specific form of the magnatriode type of tube contemplated in connection with this invention.

Fig. 2 is a diagrammatic view, similar to a transverse section through the tube of Fig. 1, to illustrate the relationship of the tube elements with respect to the magnetic field, to facilitate an explanation of the effect of this field upon the electrons emitted from the cathodes of the tube.-

Fig. 3 is a section largely diagrammatic through an iron core inductor or reactor of conventional form to illustrate how the magnetic field of such an inductor may provide the cross-magnetizing field for tubes such as shown in Fig. 1, Fig. 3 being a section taken on the line 33 of Fig. 4.

Fig. 4 is another sectional view of the diagrammatic character through the inductor of Fig. 3,

taken on the line 4-4 of Fig. 3.

Fig. 5 illustrates diagrammatically and in accordance'with certain conventions a typical-circuit organization for power conversion apparatus characteristic of this invention, assuming the inductor L of this circuit organization to be employed for providing the magnetic field for the tubes in a manner such as shown in Figs. 3 and 4.

Figs. 6A to BK are explanatory graphs or curves of voltages and currents for typical operating conditions for the circuit organization of Fig. 5, to facilitate an explanation and understanding of the operating conditions characteristic of the circuit organization of Fig. 5.

Before discussing the functions and mode of operation of the power conversion apparatus of the embodiment of the invention shown, it is expedient to explain generally the structure and operating characteristics of the so-called magnatriode type of tube, which is disclosed and claimed in other applications, such as the application of J. H. Burnett, Ser. No. 647,007, filed February 12, 1946. Fig. 1 illustrates schematically the general structure and relationship of the essential ele- 3 ments of one form of such a magnatriode, without attempting to show the various structural details, which may take various forms as disclosed in other applications, such as the application of D. V. Edwards et al., Ser. No. 726,382, filed February 4, 1947, now Patent No. 2,512,617, granted June 2'7, 1950. The ma'gnatriode type of tube assumed and shown in Fig. 1, comprises two elongated or filamentary cathodes C, which are of a suitable thermionic emissive type, and which are secured at their upper ends at spaced points t a cross member 6, and at their lower ends to separate supporting elements 6, which are insulated from each other and anchored in a stem of a suitable glass envelope E. These supporting elements 6 for the lower ends of the cathodes C extend through the envelope E with appropriate seals, in accordance with usual practice, to afford external connections or leads CL for the circuit supplying heating current to the cathodes C. It can be readily seen that this heating current flows through the cathode C in series and through an intermediate portion of the cross member 5.

The magnatriode tube structure shown in Fig. 1 also includes three fiat elongated control elements or grid bars G, which extend in parallel planes at substantially equal intervals lengthwise of the cathodes C, with one middle grid bar G located between the two cathodes C and substantially equi-distant therefrom, and the other two grid bars being located at similar distances outside of these cathodes C. The two outer grid bars G are welded to a pair of grid supporting rods 8,

of the grid supporting rods 8 serve to support the upper cross member for the cathodes C, with a suitable insulating and slidable connection between these parts, such as provided by a sleeve or bushing of steatite or like heat resistent insulating material, schematically shown and indicated at Ill. These insulating sleeves III are arranged to provide a slidable connection between the cross member 5 and the grid supporting rods 8 to permit expansion and elongation of the cathode C when heated. A cathode assembly also preferably employs an appropriate cross-section for the cathodes and a suitable means (not shown) for exerting an endwise pull on the oathode C, so as to maintain their alignment and space relationship with the grid bars G, as these cathodes C expand when heated and are subjected to the influence of the cross-magnetizing magnetic field.

The anode or plate A for the magnatriode type of tube as illustrated in-Fig. 1 comprises a boxlike structure of sheet metal around the assembly of grid bars and cathodes C, with a suitable means-for providing a supporting and external connection to this anode, such as represented by the rod l2 extending through a seal in the upper end of the envelope E and provided with 1 the usual cap to constitute an anode lead or connection AL.

The anode A, gridbars G, and associated supporting elements are prefarbly made of molybdenum, tantalum, or similar metals suitable for use in vacuum tube structures and having nonmagnetic field may act upon the electrons emitted from the cathodes C, without being materially weakened or distorted by these tube elements' or their mounting supports.

After the various tube elements have been mounted and assembled in the envelope E, with or without prior de-gassing treatment, the tube is subjected to a de-gassing and evacuation process in accordance with the usual practice for fabrication of high vacuum tubes, including the appropriate procedure for activation of the cathodes C as may be necessary, and utilizing a conventional exhaust tube connection to the inside of the envelope E (not shown), all in accordance with recognized practice.

Considering now the action and effect of. the cross-magnetizing magnetic field characteristic of this magnatriode type of tube, and referring to Fig. 2 illustrating a transverse section through the tube elements, it can be seen that the grid bars G are disposed edgewise to the surfaces of the anode A and at one side of the direct or shortest path for movement of electrons from the surfaces of the cathode C to the surfaces of the anode A. When a tube with such a structural relationship of elements is disposed in a suitable uni-directional and generally uniform magnetic field acting in a direction indicated by the arrow H in Fig. 2, i. e. transversely of the axis of the cathode C and at right angles to the surfaces of the anodes A, and generally parallel with the surfaces of the grid bars G, this magnetic field acts in accordance with well known principles to direct or focus the electrons emitted from the cathodes G into streams or beams, such as indicated by dotted lines ll in Fig. 2, which are generally parallel with the surfaces of the grid bars G. Assuming the appropriate space relationship of the parts, strength of magnetic field and potentials on the anode A and grid bars G, such a cross-magnetizing magnetic field will act to confine the electrons emitted from the surfaces of the cathodes C into streams or beams, which will afford an electron current to the anode surfaces, but do not touch the grid bars G, even though these grid bars may have a relatively high positive potential. Although the grid bars G are outside of the stream of electrons constituting the electron current to the anode A, the potential on these grid bars acts to control the emission of electrons from the cathodes, and the space charge efiect of these electrons in moving to the anode, in much thesame way as the grid of a conventional triode, negative potentials on the grid bars tending to reduce and cut off the anode current, and positive potentials on these grid bars tending to increase the anode current by neutralizing the efiect of the space charge, and also for the higher positive grid potentials increasing the potential at 'the surfaces of the cathodes and tending to increase the electron emission. In short, a positive grid potential may be employed in the magnatriode type of tube to obtain large anode currents with relatively low tube drop or anode to cathode voltages, but without any significant or substantial electron current to the grid and grid circuit losses. In this connection, the particular operating characteristics of the magnatriode type of tube are of course dependent upon a number of factors, such as the space relationship of the tube elements, the strength of the magnetic field, and the relative potentials applied to the anode and grid bars; but in general such a tube may be provided to give large anode the magnatriode tubes.

currents with low anode to cathode voltages and low tube losses by employing positive potentials on the grids, without any appreciable electron current to the grids. If still higher positive grid potentials are used for a given strength of magnetic field and anode potential, some of the electrons may reach the grid bars. The amount 01' grid current and grid circuit losses that are tolerable depend of course upon the use and application of the tube; and under some conditions a few milliamperes of grid current may be acceptable in the interests 01' increased output, over-all efliciency, or simplicity of the circuit organization.

When tubes of the magnatriode type, such as illustrated in Fig. 1A and above described, are employed in a circuit organization for power oscillators, inverters, and the like using an inductor and reactor in the anode circuits of the tubes, it is proposed in accordance with this invention to employ an inductor structure suitable for providing the cross-magnetizing magnetic field for Figs. 3 and 4 illustrate in outline one typical form of an iron core inductor for this purpose.

As shown, the inductor comprises a stacking iii of E-shaped laminations clamped together in the usual way to provide a core and magnetic circuit for the coil or coils ll of the inductor, with an airgap ill in each end leg of thecore to receive the magnatriodes T. These magnatriodes T, four as shown, are disposed flatwise in these airgap l8 of the inductor core, so that a given direction of current through the coil il, in providing magnetic flux through the end legs of the core in one direction, such as indicated by the arrow H in Fig. 3, will provide a magnetic field through the magnatriodes T in these airgaps in the proper direction for operation of these tubes, as previously explained and indicated in Fig. 2. The particular manner in which the magnatriode tubes are mounted and supported in the airgaps 18 of the inductor of the type shown in Figs. 3

and 4, with or without detachable bases and sockets, and with the appropriate electrical connections to their electrodes, together with other details of the construction and assembly of parts, are not material to this invention; and it is contemplated that any suitable expedients along this line will be employed. In this connection, for many applications it is desirable to immerse the entire inductor and the magnatriodes T in oil in accordance with common practice for electrical devices of this character, so as to provide for dissipation of heat from the tubes and more effective insulation for the parts, the tubes T being preferably disposed vertically to permit ready circulation of the all around the tube envelopes by convection.

The combination of an iron core inductor with a number of magnatriode tubes in accordance with this invention may be employed in various types of circuit organizations. Fig. illustrates a bridge arrangementof magnatriodes for a power oscillator to convert direct current to alternating current of a prescribed frequency, as a typical circuit organization of this kind. This circuit organization illustrated in Fig. 5 embodies the same general principles and mode of operation disclosed in myprior application Ser. No. 734,965, flied March 15, 1947; and no claim is made herein to the generic features of such a circuit organization.

In the circuit organization illustrated in Fig. 5, it is assumed that four magnatriodetubes TI,

TIA and'T2, T2A will be disposed in the manner previously described in the airgaps of the magnetic circuit for an inductor or reactor shown conventionally in Fig. 5 and designated L. This inductor L, which'has a relatively large inductance for reasons presently explained, is included in a direct current circuit including a suitable source of direct current, illustrated as a battery B. This direct current circuit is connected through a bridge arrangement of the magnatriode tubes Tl, TIA and T2, T2A to the primary ofa transformer TR; and the secondary of this transformer TR is connected to the terminals 20 of an alternating current outputcircuit for the oscillator. For the oscillator arrangement assumed, an adjustable capacitor C is shown connected across the secondary of the transformer TR to provide a tank circuit for the oscillator and determine its operating frequency. In the particular circuit arrangement shown in Fig. 5, the grid circuits for the magnatriode tubes Tl, TIA, etc., each include a grid. resistor 22, and also preferably a capacitor 23, for controlling the grid potential in response to flow of grid current, for reasons later explained, and are connected to corresponding secondary windings Si, SIA, S2 and .SZA of two grid transformers GT! and GT2, as can be readily seen from the drawings without detailed explanation of the circuit connections. The primaries Pi and P2 of the grid transformers G'Il and GT2 are included in the anode circuits of two pilot or control tubes VTI and VT2, energized from a suitable source indicated as a battery 25. These pilot tubes VTI and VTZ are conventional hard vacuum triodes of any suitable type having the appropriate operating characteristics.

The grid circuits of the pilot tubes VTI and VTZ in the arrangement shown in Fig. 5 are connected to the terminals 20 of the alternating cur rent output circuit, or in some equivalent manner, so that alternating voltages are applied to the grids of these pilot tubes VTI and VTZ at the operating frequency of the oscillator. As

I shown, the grids of the respective pilot tubes VTI and VT2 are connected to the terminals of the secondary of a transformer 26, having a center tap connected to the cathodes of these tubes in series with a resistor 21 and a biasing battery 28. The primary of the transformer 26 is connected by wires 29 to the alternating current circuit. As illustrated in Fig. 5, no provision is made for varying the phase relation of the grid control voltages of the pilot tubes VTI and VTZ with respect to the voltage in the alternating current circuit, but such phase shifting means may be provided, if desired, for the purposes and in the manner disclosed in my prior application Ser. No. 734,965, above mentioned.

In describing the general plan of operation for the oscillator circuit organization shown in Fig. 5, it is convenient to refer to the explanatory graphs or curves of Figs. 6A to 6H, which represent for explanatory purposes very generally the variations and time relationship of certain voltages and currents for atypical operating condition. It should be understood that these curves of Figs. 6A to 6H are not intended to be accurate as to magnitude or wave form, being in fact somewhat idealized in this respect, and are merely intended to indicate for purposes of explanation the general plan of operation and some of the factors involved. In these explanatory curves, Fig. 6A represents the alternating current output voltage of the oscillator, assumed to be sinusoidal; and Fig. 63 indicates how the grids of the pilot tubes VTI are controlled by grid control voltages derived from this output circuit. Fig. 60 indicates roughly the nature of the primary voltages for the grid transformers GTI and GT2; and Fig. 6D represents approximately the variations in grid potentials for the magnatriode tubes TI, TIA, etc. provided by such excitation of these grid transformers. Fig. GE is a repetition of the sinusoidal alternating. output voltage of the oscillator for convenient reference; and Fig. 6F represents the voltage across the magnatriode tubes .Tl, TIA, etc. Fig. 6G represents roughly and approximately the nature of the voltage across the inductor L; and Fig. 6!!

represents the blocks of current conducted by the pairs of tubes TI, TIA and T2, T2A during their conduction periods.

Disregarding the transitory conditions during which certain grid biasing potentials are established as later explained, and assuming for simplicity steady state conditions, the general operation is that the pairs of tubes TI, TIA and T2,.

T2A in the bridge arrangement are controlled by the pilot tubes VTI and VT2 to be alternately fully conductive and non-conductive in turn throughout successive half cycles of the alternating output voltage of the oscillator. The inductor L has a relatively large inductance sufiicient to maintain continuous current in the direct current circuit and in the anode circuits of the magnatriode tubes Tl, TIA, etc. throughout their conduction periods. Thus, the pairs of tubes Tl, TIA and T2, T2A act to conduct an uninterrupted series of blocks of current of essentially uniform amplitude, as indicated in Fig; 6H; and the flow of this uni-directional current through the windings of this inductor L serves to provide the cross-magnetizing field "for these magnatriode tubes TI, TIA, etc. during their conduction periods, to a degree more convenientlydiscussed later, to avoid excessive or objectionable grid currents and grid circuit losses for these magnatriode tubes.

Analyzing this operation more in detail, the alternating current voltages existing under steady state conditions across the terminals 20 of the output circuit of the oscillator supply current to the primary of the transformer 26, and induce voltages of opposite instantaneous polarity in the secondaries. of this transformer for excitation of the grids of the pilot tubes VTI and VT2. The battery 28 in the grid circuits for these tubes VTI and VT2 provides a biasing voltage for these grids, so that in effect the alternating grid voltages have an axis corresponding approximately to the negative cut off grid voltage for these tubes, as indicated in Fig. 6B. The resistor 21 in the grid circuits of these pilot tubes VTI and VT2 limits the potential which these grids may assume when the grid voltage is positive and grid current may flow. Thus, between the times to and tI for the positive half cycle of the A. C. voltage shown in Fig. 6A, the grid of the pilottube VTI has a negative potential beyond cut off between the points indicated at 4| and 42, and the voltage applied to the other pilot tube VT2 is positive, with its potential limited to some generally uniform value, such as indicated at 43 in Fig. 63 by the flow of grid current through the resistor 21. Similarly. during the next half cycle of the alternating supply voltage between the times H and t2, the pilot tube VT2 is cut ofi between the points indicated at H and 45 and is non-conductive, while the other pilot tube VTI has a positive potential on its grid is indicated at 46 and is fully conductive. Referring to the circuit arrangement shown in Fig. 5, the voltage in the anode circuits of the pilot tubes VTI and VT2 is a steady voltage provided by the battery 25, or equivalent source; and the effect of rendering the pilot tube VTI, for example, alternately conductive and non-conductive in the manner indicated in Fig. 6B, is to impress upon the primary PI of the associated grid transformer GTI essentially flat topped voltag'es, as indicated in Fig. 6C. In other words, the pilot tube VTI may be considered as acting to open and close a circuit for the battery 25 to supply current to the primary PI of the associated grid transformer GTI. The shape of the voltage induced in the secondary windings SI and SIA of this grid transformer GTI by such excitation of the primary PI depends upon the structure and operating characteristics of the transformer; and for the purposes of this invention a transformer having appropriate core dimensions and other structural features is selected for the grid transformers GTI and GT2, such that the secondary voltages are approximately fiat topped waves, such as indicated in Fig. 6D.

In the bridge arrangement assumed for the circuit organization of Fig. '5, the pairs of tubes TI and TIA for example conduct current in series from the source battery B to the output transformer TR. over a circuitwhich may be traced from the positive terminal of the battery B, through the inductor L, from the anode to the cathode of the tube TI, wires 3i and 32, upper terminal of primary of transformer TR, through this primary to its lower terminal over wires 33 and 34 to the anode of the other tube TIA to its cathode, and wires 36 and 31 from this cathode back to the other terminal of the battery B. There is a similar circuit through the other pair of tubes T2, T2A tending to send current from the battery B through the inductor L in the same direction, but in the opposite direction through the primary of the transformer TR. Thus, in

the bridge arrangement shown, each tube of the pair of tubes such as TI and TIA should be rendered conductive and non-conductive at the same time alternately with the tubes T2, T2A of the other pair. Accordingly, the secondary windings SI, SIA of the grid transformer GTI supplying grid control voltage to the pair of tubes TI, TIA, and the secondary windingsS2, 82A of the other grid transformer GT2 supplying grid control voltage to the other pair of tubes T2, T2A are so wound and connected to provide the appropriate grid voltages for these tubes to render them conductive and non-conductive at the proper times, in a manner that can be readily understood.

The alternating grid control voltages provided in this way for the pairs of magnatriode tubes TI, TIA and T2, T2A, in a manner such as represented in Fig. 6D act to render these pairs of tubes in turn fully conductive and non-conductive, and supply to the primary of the output transformer TR a series of blocks of current, such as indicated in Fig. 611. During the conductive periods of these tubes, the inductor L tends to oppose changes in current through it; and it is contemplated that this inductor will have suflicient inductance to maintain the current conducted by the pairs of tubes at a generally uniform value. The inductor L acts in this connection like any inductance to generate voltages opposing changes in the instantaneous value of the impressed voltage that would otherwise tend to increase or decrease the current through the inductance. The voltage across the inductor L under such conditions varies as indicated approximately in Fig. 6G, changing from negative to positive values in such a manner that, disregarding losses in the inductor, the areas above and below the zero.axis, such as shaded at 46 in Fig. 6G for a quarter cycle, will be substantially equal. In short, in the type of circuit organization contemplated, the inductor L of relatively large inductance, together with excitation of the grids of the magnatriode tubes TI, TIA and T2, T2A with essentially uniform positive potentials during their conduction periods, serves to make the amplitude of the blocks of current conducted by these tubes likewise essentially uniform, as indicated in Fig. 6H. Consequently, the tubes operate at a high plate efllciency, in the manner and for the reasons discussed more fully in my prior application Ser. No. 734,965 above mentioned.

Since the inductor L acts to maintain the conduction current of the tubes Tl, TIA, etc. essentially uniform throughout their conduction periods, as indicated in Fig. 6H, the tube drop or cathode to anode voltage for these tubes is generally uniform through their conduction periods; and as indicated in Fig. 6F, the voltages across these tubes vary from negative values corresponding with the A. C. voltage of Fig. 6A to some approximately uniform positive value correspond-- ing with the anode to cathode voltage required for conduction of the existing average load current at the existing grid excitation.

It may be pointed out here that it is generally preferable to select a bias for the grids of the pilot tubes VTI and VT2 such that the periods during which the induced voltages in the secondary windings S I, s I A, etc. of the grid transformers GTI and GT2 are positive and render the associated pairs of tubes TI, TIA, etc. conductive, is slightly more than 180, in order to assure that each of these pairs of tubes will be rendered conductive before conduction through the other pair is cut off, thereby providing an uninterrupted circuit path through the inductor L and avoiding excessive voltages that this inductor might otherwise generate. It should be understood that this slightoverlapping of the conduction periods of the pairs of tubes TI, TIA, T2, HA, is a preferred simple expedient to accomplish the desired purpose, and that there are usually other factors to be considered in this connection, such as the effect upon the potential of the last tube conductive by any sudden rise in the anode voltage that might be generated by the inductor L and which may act through anode to grid capacity to influence the potential of the tube conducting.

Considering now the conditions existing when the magnetic field for the pairs of magnatriode tubes Tl, TIA and T2, T2A in the circuit organization of Fig. 5 is provided by the energization of the inductor L, it can be seen that the current conducted by this inductor L during the conduction periods of these tubes is essentially uniform and corresponds with the amplitude of the blocks of current indicated in Fig. 6H flowing in the anode circuits of these tubes. It can also be appreciated that the amount of current conducted by the tubes TI, TIA, etcand flowing in the inductor depends upon the load. Under zero load conditions, as for example, when the oscillator is used for induction heating and the like and the load is not applied, the current conducted by the tubes and flowing through the l0 inductor L has the value needed to supply the circuit losses. As full load is applied, or an exist.-

ing load is increased, the tubes are called to electrons constituting the anode current into streams or beams which do not touch the control elements or grid bars for a given positive potential thereon, strength of magnetic field, and the anode to cathode voltage. With regard to the movements of the electrons emitted from the cathode, it may be considered that these electrons are subjected to the combined action of the electrostatic fields of'the existing potentials on the anodes and grids and the magnetic field of the inductor. Assuming certain load conditions and corresponding strength of magnetic field, and a certain positive grid potential where an insignificant or at least a limited number of electrons reach the grid bars of the magnatriode, a reduction in the strength of this magnetic field, and also to a degree a reduction in the anode potential with respect to the cathode, would allow more electrons to reach the grid for this same positive natriode is provided by an inductor in the anode circuit tube, if the strength of the magnetic field established by a full load current in the inductor serves to eliminate or keep within tolerable limits the grid current and grid circuit losses for a certain positive grid potential, then a decrease in the load current and the strength of the magnetic field would tend to increase materially grid circuit losses, if no change were made in the positive grid potential employed for full load conditions.

For these reasons, it is proposed in accordance with this invention to provide suitable means in the grid circuit of each of the tubes TI, TIA, etc. to limit the positive potentials the grids may assume and keep within tolerable limits the grid circuit losses under varying conditions. Referring to the typical tube structure represented in Fig. 2, when the positive potential on the grid bars G become sufficiently high for the strength of the existing magnetic field that some of the electrons from the cathode may be collected by these grid bars, these electrons tend to reduce the positive potential on the grid bars provided by the impressed voltage in the grid circuit, and at the same time these electrons tend to cause a flow of current in the grid circuit. Any inductance or resistance in the grid circuit controlling the rate at which electrons may be dissipated as current in the grid circuit, as compared with the rate at which .electrons are being collected by the grid bars, will determine the resultant potential on the grid bars for the frequency at which the oscillator is operating. It is contemplated that the impedance of the secondary windings SI,.

SIA, etc. of the grid transformers GTI and GT2 may be supplemented by such additional impedance in the grid circuit of each tube TI, TIA,

etc. as may be necessary to impose the desired limit upon the grid circuit losses by automatically reducing the positive potential on the grid of each through this resistor.

an impedance in the grid circuit-of each tube TI, TIA, etc. may have a value to create a voltage drop in the grid circuit'i'or a small grid current,

such as one milliampere, so thatwhen this voltage drop is subtracted from the impressed" grid voltage, a relatively smaller positive potential exists on the grids of these tubes than supplied by the grid circuit.

while any suitable arrangement for providing impedance in the grid circuits of the tubes TI, TIA, etc. may be employed to limit the grid cir-- previously noted, the grid voltages forthe pair of tubes TI, TIA for example are the voltages induced in the secondaries SI,.SIA of the grid transformer GTI by the abrupt energization and deenergization of the primary PI of this transformer, a voltage of one polarity being induced upon the energization of the primary PI and a voltage of the opposite polarity upon its deenergization. It may be considered that these grid voltages, irrespective of any variations in their amplitudes with respect to the cathodes of these tubes, are alternating voltages symmetrical and of equal positive and negative amplitudes about some axis such as indicated at ll in Fig. 6D.

The capacitor 23 and associated resistor 22 in the grid circuit of each of these tubes TI, TIA acts in a manner similar to the conventional grid leak and grid capacitor arrangement used for obtaining a grid biasing voltage for class C oscillators and the like, to have the effect of shifting this axis 48 of the grid voltages as electron current to the grids of these tubes causes the capacitors 23 to accumulate charges. Briefly summarizing the action of the grid leak and grid capacitor in this respect, and assuming a fiat topped grid voltage such as indicated in Fig. 6D is applied to the tube Tl for example at a time when no biasing voltage has been established. during each positive half cycle of this voltage, when a pulse of grid current may occur, the capacitor 23 receives a charge; and during the negative half cycles of the grid voltage a part of this charge on this capacitor may leak on through the grid 23. the rectifying characteristics of the grid preventing dissipation of this charge except This process is cumulative over a number of cycles, so that the charge on the capacitor builds up and the grid bias voltage increases until, under a steady state condition, the amount of the charge on the capacitor 23 lost through the resistor 22 balances the total charge received by the capacitor due to the amount of grid current flowing. Taking some amount of average grid current as beingtolerable, say in the order of a few milliamperes, a value for the resistors 2'2 may-be chosen to give a biasing voltage and a shift in the axis of the grid voltages for the tubes TI, TIA, etc. appropriate for the existing operating conditions. The limitation in the positive potential on the grids of the tubes TI, TIA, etc. by the flow of grid,

In addition to a grid biasing voltage for the tubes TI, TIA, etc. provided by the grid resistors 22 and capacitors 23, it may be desirable under some conditions to provide an additional fixed biasing voltage in these grid circuits by a battery or equivalent in an obvious manner not necessary to illustrate- Thisis because the operating characteristics of the magnatriode type of tube contemplated. such as represented in Fig. 1, may call for a negative grid potential to provide cut ofi of conduction through the tube for the peak values of the voltage across the-tube, such as indicated in Fig. 6F, which is higher thanthe positive potentials that may be employed on the grids of these tubes withoutobiectionable grid current for the magnetic field obtained by the inductor L when energized with full load current. Under such conditions, it is desirable to provide a fixed biasing voltage in the grid circuits of the tubes TI TIA to shift the axis 48 of the impressed fiat topped grid voltages to the point where, under full load conditions, the negative potential on the grids is sufiicient for out off, while the positive grid potential does not exceed the value corresponding with tolerable grid current for the strength of magnetic field provided by the inductor L; Thus, the proper selection of fixed grid biasing voltage for the existing conditions will enable the oscillator to operate at the desired high plate efficiency with insignificant or negligible grid circuit losses under full'load operating conditions; and when the load is reduced, or completely cut oi, the grid resistors 22 and capacitors 23 act to supplement the fixed biasing voltage and shift the axis of the grid voltages still further, as may be required to limit the amount of grid circuit losses to some selected and tolerable limit. The appropriate value of such a fixed biasing voltage, if needed, depends upona number of factors, such as the operating characteristics of e the tube, strength of the magnetic field provided tubes TI, TIA and T2, T2A are at some potential current in the manner characteristic of this inby the inductor L when energized by full load current, and the like; but in order that the oscillator may be self-starting, as presently dlscussed this fixed biasing voltage should be less than the negative cutoff grid potential for an anode voltage provided by the direct current source battery 13.

Briefly considering the transitory conditions existing when the oscillator is set into operation, such as by closing some switch (not shown) to connect the source battery B into the circuit, at the beginning of this transitory starting period no grid voltages are being provided by the pilot tubes VTI, VT2 and the grid transformers GTI, GT2; and the grids of the pairs of magnatriode such that both pairs of these tubes tend to conduct current in opposite directions through the primary of the output transformer TR. Due to the inherent variations in the operating characteristics of the two pairs of tubes TI, TIA, etc.,

.and variations in the impedance of their anode circuits, which may be exaggerated if desired. there is a small resultant current through the primary of the transformer'TR in one direction or the other. Such pulse of small current in the .primary of I the transformer TR produces a flux change in its core to-give. a voltage surge in its secondary and the tank. circuit for the oscillator, which is also accompanied by a change of current in the primary of the transformer 26 to vary the grid'potentials of the pilot tubes VTI and VT2. Such change in the grid potentials of the pilot tubes VTI and VT2 varies their anode currents and results in a current change in the primaries 13 PI and P2 of the grid transformers GTI and GT2, which in turn changes the potentials on the grids of the pairs of magnatriode tubes Tl, TIA and T2, TZA, and tends to make one pair of these tubes more conductive and the other pair less a conductive. The net result of such an action occurring upon initial connection of the source battery B into the circuit, which becomes cumulative as the tank circuit of the oscillatory, is that the voltages and currents quickly build up to the steady state condition previously discussed, in a manner similar to that which occurs in starting a conventional oscillator with a tuned plate circuit, so that after a brief period of transitory starting operation, the pairs of tubes Tl, TIA and T2, T2A are rendered alternately fully conductive and non-conductive in turn. 7

In the particular type of magnatriode tube assumed and illustrated in Fig. 1, a cross-magvided by the load current in the inductor .L, as

proposed in accordance with this invention, a temporary overload condition or surge of excessive load current, not ordinarily injurious to an electron discharge tube, might be damaging to the tubes under such circumstances by providing a magnetic field too strong for the cathodes to withstand. Accordingdy, it is preferred to use in the organization of this invention an inductor L, which is designed in accordance with well known principles to be saturable at some predetermined load current corresponding with the maximum magnetic field suitable for the tubes being used, so that any larger load current existing for any reason will not increase the strength of the magnetic field and tend to break the cathodes.

From the foregoing, it can be seen that this invention provides a simple and efilcient way for utilizing an inductor L, constituting a desirable element in the power conversion circuit organization contemplated, to provide the magnetic field for the tubes of the magnatriode type likewise used to advantage in such a circuit organization, with the appropriate control of the grid potentials of these tubes to take care of variations in the strength of the magnetic field for the tubes -due to changes in load current through the inductor. In general, the attributes and advantages of this distinctive combination or organization of elements, from the standpoint of simplicity, operating efficiency, and the like, can be readily appreciated from the previous discussion of the functions'and mode of operation of the particular embodiment of the invention shown and described.

The present invention in its fundamental as-' pects may be embodied in a wide variety of forms in practice; and it should be understood that various adaptations, modifications, and additions may be made in the circuit organization and structures for the inductor and tube herein illustrated and described to represent one specific embodiment of the invention, without parting from the scope of the invention.

14 What I claim is: 1. A circuit organization for electron discharge tubes comprising in combination, a hard vacuum tube having a thermionic emissive cathode and anode, a control element for said tube disposed adjacent an allotted direct path for electrons moving from the cathode to anode, an inductor having its winding included in the anode circuit of said tube and having an airgap, said tube being disposed in the airgap of'said inductor in a position where the magnetic field created by the anode current through the inductor acts to focus the electrons emitted from the cathode into said allotted path to miss said control element even though it is at a relatively high positive potential, and means for applying input'potentials to said control element to control the electron emission of said cathode and the spacecurrent.

2. In power conversion devices employing electron discharge tubes, the combination of a plurality of hard vacuum tubes each having a thermionic emissive cathode and an anode, a control element for each tube disposed adjacent a path for electrons moving from the cathode to the anode, an inductor having its windings included in the anode circuits of said tubes having an airgap and sufficient inductance to maintain continuous current through it as the tubes are alternately rendered conductive, said tubes being disposed in the airgap of said inductor and subjected to the magnetic field created by the current in said inductor to direct the electrons emitted from the. cathode into a beam to the anode and out of contact with said control element, and means for applying positive and negative potentials to said control elements of said tubes alternately to control the electron emission gfbzach cathode and the space current of its 3. In power conversion apparatus including hard vacuum electron discharge tubes, the combination of a tube having a onic emissive cathodes between opposing surfaces of an anode in anevacuated envelope, a plurality of control elements in said envelope disposed adjacent saidcathodes and the direct paths for movement of electrons from the oathodes to the anode, and an iron core inductor having its windings included in the anode circuit of said tube and having an-airgap, said tube being disposed in the airgap of said inductor with the magnetic field of its core acting to focus electrons moving from the cathode tothe anode into beams missing said control elements in spite of relatively high positive potentials thereon.

4. Power conversion apparatus employing electron discharge tubes and comprising in combination, a tube having a filamentary thermionic cathode between opposing surfaces of an anode, fiat grid bars on opposite sides of said cathode adjacent the direct path for movement of electrons from the cathode to the anode, said tube elements being enclosed in a highly evacuated envelope, and an inductor having an airgap in its magnetic circuit and a winding included in the anode circuit of said tube, said tube being disposed in the airgap of said inductor with its spite of a relatively high positive potential thereon.

plurality of thermidisposed in the airgap of said inductor in. a

anode surfaces, said tubes being disposed-in the l 5. Power conversion apparatus or the character described comprising in combination, a hard vacuum electron discharge tube having a control element for governing anode current, an inductor included in the anode-circuit of said tube 5 and havingan airgap in its core, said tube being position where the magnetic field or the nt 2 through the inductor acts to direct electrons in paths missing said control element in spite of a m positive potential thereon, the positive potential which said control element may assume without significant electron current being dependent upon the strength of said magnetic field, means for applying positive and negative voltages to said control element to render said tube conductive and non-conductive, and means including an impedance in the circuit of said control element for reducing its positive potential when grid current flows. I

6. Power conversion apparatus of the character described comprising in combination, an alternating current circuit, a direct current circuit, a pluralit of high vacuum electron discharge power tubes. having control grids for governing anode current, a rectifying circuit organization including said alternating circuit and said direct current circuit and said tubes, said circuit organization including a relatively large inductanee in said direct current circuit, means ineluding pilot tubes controlled from said alter-. nating current circuit for exciting the grids of said tubes with essentially flat topped alternating current voltages of positive and negative values and thereby render said tubes-altemately fully conductive and non-conductive in turn, means for providing a magnetic field for each 01 said power tubes to prevent electron current fiow to their control grids for a range of relatively high positive potentials thereon, and a resistor and 4 capacitor in multiple in the grid circuit of each tube for providing a negative biasing voltage to limit the positive potential assumed by the grid under the influence of said flat topped grid control voltages and in response to the flow 01' grid current.

'7. Power conversion apparatus of the character described comprising in combination, an electron discharge tube of the type controlling anode current in accordance with the positive potential of a control element, said tube when disposed in a magnetic field having the electron current to its control element dependent upon the positive potential of the grid and the strength of said magnetic field, an iron core inductor included in the anode circuit of said tube ior providing said magnetic field for said tube, means for exciting the control element of said tube with positive and negative voltages to render said tube conductive and non-conductive, and means associated with the circuit for the control element of said tube for providing a negative biasing voltage in response to the flow of grid current, and thereby reduce the positive potential on the control element when the magnetic field is decreased by a reduction in anode current.

8. Power conversion apparatus comprising in combination, an inductor having an airgap in its magnetic circuit, a plurality of electron discharge tubes each having a thermionic emissive cathode and anode surfaces in a highly evacuated envelope, a control element for each tube within said envelope disposed outside of the direct path for electrons moving from the cathode to the iairgap of said inductor with its magnetic field acting to direct electrons emitted from the cathode into beams reaching said anode surfaces but missing said control element, a circuit organization providing anode circuits for said tubes including said inductor and acting to supply current in the same direction to-said inductor as said tubes are rendered conductive, and means for applying positive and negative potentials to the control elements of said tubes to render them alternately conductive and non-conductive in urn.

9. A power conversion device of the character described comprising in combination, a plurality of electron discharge tubes each including a thermionic emissive cathode and an anode, a

control element for each tube disposed outside the direct path for electrons moving from the cathode to the anode, an inductor or relatively '20 large inductance having an airgap in its magnetic circuit, anode circuits for said tubes including said inductor, and control means for providingpositive and negative potentials on the control elements of said tubes to render them alternately conductive and non-conductive in turn, said control means acting to maintain conduction through each tube for a prolonged period approximately until conduction through another tube is started and thereby provide continuous current through said inductor, said tubes being disposed in the airgap of said inductor and being subjected to the magnetic field created by the flow 01' current through the inductor to prevent electron current to the control elements of each tube for relatively high positive potentials thereon.

. 10. Power conversion apparatus employing electron discharge tubes of the hard vacuum type comprising in combination, a plurality of tubes each having a plurality of thermionic emissive cathodes and anodes in a. highly evacuated envelope, a plurality of grid bars for each tube disposed on opposite sides of said cathodes outside the direct path for movement of electrons from said cathodes to the anode surf ces, an

iron core inductor having an airgap in its magnetic circuit and a winding included in the anode circuits of said tubes, said tubes being disposed in said airgap of the inductor with the I thereon.

11. Power conversion apparatus of the character described comprising in combination, av

plurality of high vacuum electron discharge tubes having control grids for governing anode currents, an inductor having an airgap in" its I core and a winding included in the anode circuits of said tubes, said tubes being located in the airgap of said inductor in position where the magnetic field of the current through the inductor winding acts to .prevent electrons reaching the grids of said tubes for a range in-posi-.

tive potentials corresponding with the strength of said magnetic field, means for providing essentially fiat topped positive and negative grid control voltages in the grid circuits of said tubes to render them alternately conductive and nonconductive in turn, and a resistor and capacitor in the grid circuit of each tube for providing a negative grid biasing voltage in response to the flow of grid current when the strength of the magnetic field of said inductor permits electron current to reach said grid.

12. Power conversion apparatus of the character described comprising in combination, a plurality of high vacuum electron discharge power tubes having grids for controlling anode current, an alternating current circuit, a direct current circuit, a rectifying circuit organization interconnecting the anode circuits of said tubes with said alternating current circuit and said direct current circuit, an inductor of relatively large inductance included in said direct current circuit, means for exciting the grid circuits of said tubes with essentially fiat topped alternating grid control voltages of positive and negative values for rendering said tubes alternately fully conductive and non-conductive in turn, means for providing a magnetic field for each of said power tubes to prevent electron current to their respective control grids for a range of relatively high positive potentials thereon, and means including a resistor in the grid circuit of each tube and acting in response to the flow of grid current to limit the positive potential assumed by that grid under the control of said grid control voltages.

13. Power conversion apparatus of the character described comprising in combination, a plurality of electron discharge power tubes each having a thermionic emissi've cathode and anode in a highly evacuated envelope, a control grid for each tube capable of controlling anode current, means including an inductor for providing a magnetic field for each of said power tubes to prevent electron current fiow to their control grids for a range of relatively high positive potentials thereon, a circuit organization including an alternating current circuit and a direct current circuit including said inductor and the anode circuits of said tubes, a transformer having opposing secondary windings included. in the grid circuits of said tubes, a control triode having an anode circuit including the primary winding of said transformer and a source of steady voltage, and means energized from said alternating current circuit for governing the grid of said triode to provide intermittent energization of the primary winding of said transformer.

14. Power conversion apparatus comprising in combination, an inductor having an airgap in its magnetic circuit, a plurality of electron discharge tubes disposed in the' airgap of said inductor, each of said tubes comprising a thermionic emissive cathode and anode in a highly evacuated envelope, each of said tubes having a 'grid element insaid envelope capable of con- 18 potentials to the grid elements of said tubes to render them fully conductive and non-conductive alternately, and means including a control triode governed from said alternating current circuit for intermittently energizing the primary Winding of said grid transformer.

15. Power conversion apparatus of the character described comprising in combination, an alternating current circuit, a direct current circuit, a plurality of electron discharge power tubes of the hard vacuum type each having a grid for controlling anode current, a circuit organization connecting the anode circuits of said tubes in a rectifying bridge arrangement between said alternating current and said direct current circuit, means including an inductor of relatively large inductance with its windings connected in the direct current circuit for providing a magnetic field for each of said power tubes to prevent electron current fiow to their control grids for a range of relatively high positive potentials thereon, grid transformers having opposing secondary windings included in corresponding grid circuits of said tubes, and means including hard vacuum control triodes having grid circuits governed from said alternating current circuit for intermittently energizing the primary windings of said grid transformers alternately and thereby provide essentially flat topped grid control voltages for the grids of said tubes.

16. Power conversion apparatus of the character described comprising in combination, two pairs of high vacuum electron discharge power tubes having grids for controlling anode current, an alternating current circuit, a direct current circuit, a circuit organization connecting the anode circuits of said tubes in a rectifying bridge arrangement between said alternating current circuit and said direct current circuit, an inductor of relatively large inductance with its windings connected in said direct current circuit and located adjacent said power tubes for providing a magnetic field for each of said power tubes having a direction acting to prevent electron current flow to their respective grids when relatively high positive potentials are applied thereto, grid transformers having opposing secondary windings included in associated grid circuits of said grid tubes, means for intermittently energizing the primary windings of said grid transformers alternately in timed relation to the voltage in said alternating current circuit, said grid transformers providing in their secondary windings essentially uniform positive and negative grid control voltages to render said pairs of tubes alternately conductive and nonconductive in turn, and a capacitor shunted by a resistor and included in the grid circuit of each tube for providing a negative biasing voltage in response to the flow of grid current.

DONALD V. EDWARDS.

REFERENCES CITED The following references are of record inthe file of this patent:

UNITED STATES PATENTS Number .Name Date 1,657,574 Hazeltine Jan. 31, 1928 1,803,184 Hazeltine Apr. 28, 1931 2,056,412 Spencer 0ct.-6, 1938' 2,248,712 Litton i July 8, 1941 2,333,977 Skellett Oct. 6, 1948 

